Power take-off (PTO) units are well known in the art and most commonly used with sources of rotational power, such as engines and transmissions, for rotatably driving an accessory such as a pump which, in turn then operates any number of hydraulically driven devices such as lifting devices, winches, and the like.
Frequently, the PTO unit further includes a clutch assembly, generally of the fluid pressure actuated type, for selectively disconnecting the output shaft from the input gear, thus permitting selective and/or intermittent operation of the driven accessory without having to stop the vehicle engine. Thus, when the clutch assembly is engaged, the output shaft is rotatably driven by the input. Conversely, when the clutch assembly is disengaged, the output shaft is decoupled from the input gear and the driven device is not operated by the engine, etc.
Since operation of the PTO unit can generate undesirable friction and heat, the PTO unit is generally provided with a considerable quantity of lubricating fluid. However, it has been determined that the relatively viscous nature of the lubricating fluid can cause the output shaft to continue to be at least partially rotatably driven, even though the clutch assembly has been disengaged. This is particularly the case during cold weather operation when the lubricating fluid is cold and viscous, such as when the vehicle is initially started. Naturally, such rotation of the output shaft of the PTO unit, after the clutch assembly has been disconnected, is undesirable.
This noted problem has been addressed in the prior art by the addition to the PTO unit output shaft, of a brake system, such as a drag brake assembly. One such prior art device, namely the automatically actuated drag brake assembly set forth in U.S. Pat. No. 6,497,313 B1, to Blalock, which is also assigned to the assignee of the present invention, utilizes a brake piston that is coaxially aligned with an end face of the output shaft and is normally urged into frictional end abutment therewith via a wave spring interposed between one end of the piston and an adjacent bearing end cap, thereby braking the output shaft. A fluid pressure operated clutch, interposed between the input gear and the output shaft, upon actuation, overcomes the bias of the spring and thus couples the output shaft to the input gear. While workable, it has been determined that the available frictional braking surface is not sufficient to ensure complete rotational stoppage of the output shaft under all operating conditions. Thus, the present invention sets forth an improved automatic drag brake for a PTO unit output shaft that overcomes the noted insufficient stopping power of this prior art device.
The patent literature includes a large number of PTO unit drag brake devices as well as devices that utilize frictionally engaging cone-type brake members and additionally include: U.S. Pat. No. 3,035,458 to Wickman; U.S. Pat. No. 3,872,954 to Nordstrom et al.; U.S. Pat. No. 4,175,649 to Monks; U.S. Pat. No. 4,310,080 to Jarvis et al.; U.S. Pat. No. 4,567,965 to Woodruff; U.S. Pat. No. 4,706,520 to Sivalingam; U.S. Pat. No. 5,437,355 to Tagaki; U.S. Pat. No. 5,542,306 to Fernandez; and U.S. Pat. No. 6,142,274 to Warner. However, none of these prior art structures, pertains to the use of a cone-type brake, having interacting truncating frusto-conical mating surfaces, where the stationary reaction member, having one of the noted frusto-conical surfaces, is located on the inner surface of the inside diameter of one of the PTO unit bearing end caps.